Well then I don't know what to tell you. Obviously as you've been told by several posters here its common to get asked to wait 15 minutes after getting any vaccine. I know its happened to me at my doctors office, and at Walgreens.
Just because it hasn't happened to you, apparently ever, doesn't mean it doesn't happen. Maybe ask your doctor, who you know socially anyways, why they don't ask you to stay 15 minutes after been given a vaccine.
I was also IM'ed by a poster here who is a CM whose only lifelong vaccination experience has been getting a flu shot from the third-party medical outfits that Disneyland pays to give out flu shots to 30,000 CM's every year, and that CM said they've never been asked to wait 15 minutes after getting a flu shot. And in 2015 they also got a free Measles shot from Disneyland after the Measles outbreak. No 15 minute observation period was offered then, either.
According to this person, flu shots are given out every autumn in the ballrooms of the Disneyland Hotel or Grand Californian Hotel for any CM who wants it. You also get a full medical screening for free; height/weight, blood cholesterol levels, blood pressure, etc. But once you get the flu shot, you are done, and you just leave the ballroom and go back to work at the Jungle Cruise. No 15 minute medical observation is offered.
I think it's hysterical that CM's keep IM'ing me to tell me the real dirt on stuff because they think I'm trustworthy. This is not the first time this has happened, and it ranges from random topics like flu shots to Krazy Karen celebrities who throw their name around when their nanny and their sister don't get into the park for free.